1. Field of Invention
The invention relates to a data encoding method and, in particular, to an encoding in a recording media that simplifies the actual operation loading in the look-ahead calculation, thereby speeding up the encoding procedure.
2. Related Art
The encoding mechanism for recording media is mainly used to encode data words using specific encoding procedures into code words so as to be stored in an ordered way within a small storage space on a recording media. One can use a set of specific decoding rules to restore the original data words.
In the encoding procedure, the coding rate directly affects the data capacity that can be stored in a recording media. Therefore, an encoding method of high coding rate has been the goal of related fields. In the past, trying to increase the coding rate results in the decrease in selectable code words. And this kind of encoding method further has worse code word sequence properties, particularly in the DC component control ability. To enhance the code word sequence properties, an encoding method combines the look-ahead calculation has been created to perform encoding procedures.
The so-called look-ahead calculation is as follows. First, one computes paths for several successive data words in advance. An optimal path is searched using predetermined conditions, and then the code words of the optimal path are then used for encoding. Generally speaking, the longer the length of look-ahead is, the better properties the code word sequence will have. And the computation loading increases exponentially with the length of the look-ahead at the same time. This will inevitably results in the delay of the encoding speed.
As the encoding method with look-ahead calculation becomes more popular, it is necessary to improve its calculation algorithm. It is imperative to simplify the computation loading of possible paths in the look-ahead calculation, thereby increasing its efficiency and practicality.